A scroll compressor generally comprises a compressor with a pair of compression chambers which consecutively move between a fixed wrap of a fixed scroll and an orbiting wrap of an orbiting scroll. When compared to other compressors, the scroll compressor exhibits excellent vibration and noise characteristics. This is because a refrigerant is alternately sucked into the two compression chambers, and then is consecutively compressed to be discharged.
A behavior characteristic of the scroll compressor is determined by the fixed wrap and the orbiting wrap designs. The fixed wrap and the orbiting wrap may be formed in any shape. However, each of the fixed wrap and the orbiting wrap is generally formed as an involute curve having a constant wrap thickness. An involute curve is a curve corresponding to an orbit formed by the end of a taut thread when unwinding the thread wound on a circle of any radius. When using the involute curve shape, a capacity change ratio is constant since a wrap thickness is constant. Therefore, to achieve a high compression ratio of the scroll compressor, the number of windings of the wrap has to be increased or the height of the wrap has to be increased. However, when the number of windings of the wrap is increased, the compressor's size may become too large. Furthermore, when the height of the wrap is increased, the intensity of the wrap is lowered and degrades reliability.
In order to solve these problems, the conventional scroll fluid machine (Japanese Patent Application Publication No. 6-137286) has disclosed a method capable of enhancing a compression ratio without increasing the number of windings of a wrap. This is accomplished by forming the wrap in an involute curve, where a wrap thickness becomes thicker by a predetermined ratio toward an inside initial end (discharge side end) from an outside terminal end (suction side end), or by forming a height of a discharge side end plate (i.e., wrap height) to be higher than a height of a suction side end plate, while maintaining a wrap thickness of a scroll. To design a wrap such that its thickness can be increased towards a discharge side end, the wrap thickness of a suction side end must first be determined. This may lower the degree of design freedom of the wrap, and thus may cause limitations in designing a compression ratio of the scroll compressor in accordance with a desired refrigerating capacity.
Furthermore, in the case of increasing a height of a discharge side end plate while constantly maintaining a wrap thickness of a scroll, a discharge side wrap intensity with respect to a compression ratio is low. This may cause damage to the wrap. Furthermore, since a sealing area with respect to a compression ratio is narrow due to a thin wrap thickness, leakage in an axial direction may also occur.